PROJECT SUMMARY: Gliomas are the most frequently occurring primary malignant brain tumors, with glioblastoma multiforme (GBM) being one of the most fatal and treatment-refractory of all cancers. New treatments are urgently needed. First-generation oncolytic Herpes Simplex Viruses (1st gen oHSVs) used in Phase I clinical trials were safe and produced a 50% response rate however, only a minority of patients had a durable anti-tumor response. Analysis of the 1st gen oHSV-treated glioma specimens shows that increased antiviral and immunostimulatory activity in the tumor directly correlates with longer survival in the Phase Ib study. The 1st Gen oHSVs were designed to restrict viral replication and therefore could not maintain infection or sustain an antiviral immune response. To improve oHSV antitumor activity, we have developed a next- generation oHSV, C134, with enhanced immunostimulatory activity. C134 is designed to activate antiviral cellular pathways important for amplifying the immune response and to improve viral replication in tumor cells. While it shares a similar safety profile as the 1st gen oHSVs, C134 has superior anti-tumor efficacy in pre- clinical models. Murine studies also show that C134 more effectively induces T cell and antigen presenting cell responses that are associated with improved patient survival in the Phase Ib studies. We will test our hypothesis that ?C134 is safe and induces immune activity that enhances the anti-tumor response in patients with recurrent malignant glioma? by the following aims: Aim 1: To conduct a Phase I clinical trial to determine a safe C134 (IND 17296) dose in patients with recurrent malignant glioma. Hypothesis: Intratumoral administration of C134 is safe in patients with recurrent malignant gliomas. We are ready to start our Phase I trial. Our clinical grade C134 has received regulatory approval from the NIH-Recombinant DNA Council (RAC) and FDA-Investigational New Drug (IND#17296). C134 will be intratumorally-administered to patients using a Continual Reassessment Method (CRM) design and will be monitored for C134 safety and tolerability. AIM 2 To monitor immune response changes associated with oHSV mediated anti-tumor responses among C134-treated patients. Hypothesis: C134-induced antiviral and Th1 immune activity contribute to anti- tumor efficacy and can be inferred from peripheral blood samples. Our past clinical trial results indicate that oHSV-induced immune activity is associated with improved survival. We will therefore monitor patient's peripheral blood (immunophenotyping and cytokine) after C134-treatment and define how immune response changes relate to anti-tumor response. Studies will also examine how sustained viral activity and T cell clonal changes contribute to the C134-anti-tumor response. Impact: Successful completion of these studies is the first step in establishing an effective therapy for an incurable tumor and would provide a way to monitor and potentially enhance the virotherapeutic response.